# Measuring transmitted-to-incident ratio of an inductor

Question asked by te123 on Apr 24, 2009
Latest reply on Apr 25, 2009 by te123
Hello all,

I have a basic and related question to the topics in this forum so I thought I would ask here. I am a novice user of an Agilent 8753ES network analyzer (with bridge 86205A) which has not been used in a number of years and currently we do not have anyone in our (academic) department who knows how to use it.

I would like to measure the transmitted-to-incident voltage ratio (S21, I believe) through a coil of wire (an inductor) over a 300 kHz – 1 GHz frequency range. My purpose is to try to determine how much voltage loss would be expected at high frequencies, since its impedance should increase with frequency. This inductor has two wires accessible to it (input and output) and can be thought of as being similar in appearance to the Greek capital letter “omega”. Based on literature I thought that it would be most appropriate to use the “B/R” ports to make this measurement. However, my problem is that I cannot seem to find the best means of interfacing the inductor to the network analyzer. Both the “R” and “B” ports appear to have two connections (SMA, +/-), yet I only have two cables to connect to.

Using dual alligator clips at the end of both the B and R connectors, I was able to simultaneously clip the start and end of the inductor to both the B and R connectors. However, when plotting the transmission-to-incident voltage ratio, I found some positive dB values, which did not make sense to me (please see my attached plot, calculated using: dB=20*log10(SQRT((Real^2)+(Imag^2)), which I found from the analyzer manual). Thus I do not believe this to be the correct method.

So I would like to ask:

1) Is it possible to make transmitted-to-incident measurements using a device with only two cables (i.e. “one port”)?
2) If it is possible (particularly with an 8753ES), what would be a recommended method of making this kind of measurement, and/or impedance measurements up to 1 GHz?

Thank you very much for your thoughts and I would like to apologize for my novice and verbose question. I am looking forward to receiving any and all feedback. Thanks!